In a Document level allowance (ibg-20) where Tax category code (ibt-95) is "O (Outside of scope of tax)" shall not contain a Document level allowance tax rate (ibt-96).
cac:AllowanceCharge[cbc:ChargeIndicator=false()]/cac:TaxCategory[normalize-space(cbc:ID)='O'][cac:TaxScheme/normalize-space(upper-case(cbc:ID))='VAT'](not(cbc:Percent))